A carpenter chops down a tree...
He brings the tree in and makes two chairs intending to sit on them by the fireplace.
But before he has a chance to sit on them, his brother walks in and breaks one of the chairs apart to make a fire.
The carpenter says "That was not the chair's purpose!"
His brother says "This morning I was going to chop down that tree for firewood but something else came up."
The carpenter says "But that was not the chair's purpose!"
His brother sits down in the remaining chair and says "I know. Do you know what is not this chair's purpose? Everything."
"Need" is just a fiction. As is "should", "must", "value" and "importance".